The S(N)2 reactions at nitrogen center (S(N)2@N) play a significant role in organic synthesis, carcinogenesis, and the formation of some environmentally toxic compounds. However, the S(N)2@N reactions specifically for neutral compounds as nucleophiles are less known. In this work, reactions of dimethylamine (DMA) and F- with NH2Cl were investigated as model reactions to validate an accurate functional from 24 DFT functionals by comparing with the CCSD(T) reference data. M06-2X functional was found to perform best and applied to systematically explore the trends in reactivity for halides (F- and Cl-) and simple amines toward the substrates NH2Cl and NHCl2 (S(N)2@N) as well as CH3Cl and CH2Cl2 (S(N)2@C). The computational results show that the backside inversion channel dominates most the S(N)2@N reactions except for the case of F- + NHCl2, which reacts preferentially via proton transfer. The overall activation free energies (Delta G(double dagger)) of the inversion channel for the S(N)2 reactions of F- and Cl- with chloramines are negative, whereas those for amines as nucleophiles are around 30-44 kcal/mol. The S(N)2@N reactions for all the nucleophiles investigated here are faster than the corresponding S(N)2@C. Moreover, amines react faster when they have a higher extent of methyl substitution. Additionally, the energy gap between the HOMO of nucleophile and LUMO of substrate generally correlates well with Delta G(double dagger) of the corresponding S(N)2 reactions, which is consistent with previous results.